本节书摘来异步社区《Java 2D游戏编程入门》一书中的第8章，第8.4节，作者：【美】Timothy Wright（莱特），更多章节内容可以访问云栖社区“异步社区”公众号查看。
位于javagames.prototype包中的PrototypeAsteroidFactory，包含了3个大的、3个中型的和3个小的小行星，它们都是使用编辑器并粘贴到代码中设计的。给定一个位置，这3个方法生成一个随机数来选择所返回的小行星：
createLargeAsteroid( Vector2f position ) createMediumAsteroid( Vector2f position ) createSmallAsteroid( Vector2f position )``` 第一个方法mirror()，用来沿着x轴和y轴翻转模型，以便模型有多个独特的版本。// PrototypeAsteroidFactory.javaprivate Vector2f[] mirror( Vector2f[] polygon ) { Vector2f[] mirror = new Vector2f[ polygon.length ]; float x = rand.nextBoolean() ? 1.0f : -1.0f; float y = rand.nextBoolean() ? 1.0f : -1.0f; Matrix3x3f mat = Matrix3x3f.scale( x, y ); for( int i = 0; i < polygon.length; ++i ) { mirror[i] = mat.mul( polygon[i] ); } return mirror;}`就像在执行视口矩阵乘法的时候使用矩阵来翻转y轴一样，通过乘以-1来翻转x或y轴的值，以缩放模型。
package javagames.prototype; import java.util.Random; import javagames.prototype.PrototypeAsteroid.Size; import javagames.util.Matrix3x3f; import javagames.util.Vector2f; public class PrototypeAsteroidFactory { private static final Vector2f[][] LARGE = { { // Large 0 new Vector2f(-0.029733956f, 0.283255100f), new Vector2f(-0.183098610f, 0.111111104f), new Vector2f(-0.230046930f,-0.057902932f), new Vector2f(-0.092331770f,-0.139280080f), new Vector2f( 0.117370844f,-0.142410040f), new Vector2f( 0.161189320f,-0.048513293f), new Vector2f( 0.151799680f, 0.067292630f), new Vector2f( 0.195618150f, 0.129890440f), new Vector2f( 0.017214417f, 0.158059480f), }, { // Large 1 new Vector2f(-0.001763641f, 0.325800420f), new Vector2f(-0.082892360f, 0.220339000f), new Vector2f(-0.227513200f, 0.065913380f), new Vector2f(-0.206349200f,-0.141242860f), new Vector2f(-0.061728360f,-0.080979230f), new Vector2f( 0.061728418f,-0.167608260f), new Vector2f( 0.192239940f,-0.092278720f), new Vector2f( 0.167548480f, 0.126177010f), new Vector2f( 0.107583820f, 0.269303200f), }, { // Large 2 new Vector2f( 0.176838760f,-0.107981205f), new Vector2f(-0.070422530f,-0.076682330f), new Vector2f(-0.220657290f,-0.123630640f), new Vector2f(-0.273865400f, 0.048513293f), new Vector2f(-0.186228510f, 0.086071970f), new Vector2f(-0.214397490f, 0.223787190f), new Vector2f(-0.026604056f, 0.148669780f), new Vector2f( 0.104851365f, 0.220657290f), new Vector2f( 0.211267590f, 0.032863855f), }, }; private static final Vector2f[][] MEDIUM = { { // Medium 0 new Vector2f(-0.045383394f, 0.186228510f), new Vector2f(-0.167449180f, 0.123630700f), new Vector2f(-0.067292630f, 0.039123654f), new Vector2f(-0.107981205f,-0.073552370f), new Vector2f( 0.057902932f,-0.073552370f), new Vector2f( 0.133020280f, 0.098591566f), }, { // Medium 1 new Vector2f(-0.023474216f, 0.189358350f), new Vector2f(-0.107981205f, 0.107981205f), new Vector2f(-0.129890440f,-0.098591566f), new Vector2f( 0.020344257f,-0.120500800f), new Vector2f( 0.139280080f,-0.001564979f), new Vector2f( 0.076682330f, 0.092331770f), new Vector2f(-0.007824719f, 0.095461670f), }, { // Medium 2 new Vector2f(-0.064162790f, 0.158059480f), new Vector2f(-0.173708920f, 0.126760600f), new Vector2f(-0.142410040f, 0.023474216f), new Vector2f(-0.039123654f, 0.029733956f), new Vector2f( 0.010954618f,-0.035993695f), new Vector2f( 0.117370844f, 0.023474216f), new Vector2f( 0.117370844f, 0.120500800f), new Vector2f(-0.001564979f, 0.092331770f), }, }; private static final Vector2f[][] SMALL = { { // Small 0 new Vector2f(-0.048513293f, 0.057902990f), new Vector2f(-0.073552430f,-0.042253494f), new Vector2f( 0.004694819f,-0.035993695f), new Vector2f( 0.042253494f, 0.026604056f), new Vector2f(-0.001564979f, 0.082942130f), }, { // Small 1 new Vector2f( 0.067292690f, 0.007824719f), new Vector2f(-0.029733956f,-0.076682330f), new Vector2f(-0.067292630f,-0.042253494f), new Vector2f(-0.061032890f, 0.082942130f), new Vector2f( 0.032863855f, 0.111111104f), }, { // Small 2 new Vector2f(-0.007824719f, 0.089201870f), new Vector2f(-0.114241004f, 0.001564979f), new Vector2f(-0.004694819f,-0.067292690f), new Vector2f( 0.039123654f,-0.039123654f), new Vector2f(-0.014084518f, 0.020344317f), }, }; private PolygonWrapper wrapper; private Random rand; public PrototypeAsteroidFactory( PolygonWrapper wrapper ) { this.wrapper = wrapper; this.rand = new Random(); } public PrototypeAsteroid createLargeAsteroid( Vector2f position ) { PrototypeAsteroid asteroid = new PrototypeAsteroid( wrapper ); asteroid.setPosition( position ); asteroid.setPolygon( getRandomAsteroid( LARGE ) ); asteroid.setSize( Size.Large ); return asteroid; } public PrototypeAsteroid createMediumAsteroid( Vector2f position ) { PrototypeAsteroid asteroid = new PrototypeAsteroid( wrapper ); asteroid.setPosition( position ); asteroid.setPolygon( getRandomAsteroid( MEDIUM ) ); asteroid.setSize( Size.Medium ); return asteroid; } public PrototypeAsteroid createSmallAsteroid( Vector2f position ) { PrototypeAsteroid asteroid = new PrototypeAsteroid( wrapper ); asteroid.setPosition( position ); asteroid.setPolygon( getRandomAsteroid( SMALL ) ); asteroid.setSize( Size.Small ); return asteroid; } private Vector2f[] getRandomAsteroid( Vector2f[][] asteroids ) { return mirror( asteroids[ rand.nextInt( asteroids.length ) ] ); } private Vector2f[] mirror( Vector2f[] polygon ) { Vector2f[] mirror = new Vector2f[ polygon.length ]; float x = rand.nextBoolean() ? 1.0f : -1.0f; float y = rand.nextBoolean() ? 1.0f : -1.0f; Matrix3x3f mat = Matrix3x3f.scale( x, y ); for( int i = 0; i < polygon.length; ++i ) { mirror[i] = mat.mul( polygon[i] ); } return mirror; } }``` RandomAsteroidExample位于javagames.prototype包中，如图8.10所示，它使用PolygonWrapper、PrototypeAsteroid和PrototypeAsteroid Factory，来生成在屏幕上随机飞来飞去的陨石。 <div style="text-align: center"><img src="https://yqfile.alicdn.com/b714c45b53653458cc5392685ac60b1e1273e94d.png" width="" height=""> </div> getRandomAsteroid()方法创建了一个随机的位置，然后选择一个随机的大小：small、medium或large。记住，工厂的每一个方法都从3种不同的多边形模型中针对每个大小选取一个模型，并且为每个模型生成4个镜像的版本。每个多边形有4个镜像，每个大小有3个形状，共有3种不同的大小，因此，共有36种不同的模型。 还应该注意，由于PrototypeAsteroid使用了新的Utility.fillPolygon()方法，Graphics对象强制转型为一个Graphics2D对象。// RandomAsteroidExample.javaprotected void render( Graphics g ) { super.render( g ); g.drawString( "Press ESC to respawn", 20, 35 ); Matrix3x3f view = getViewportTransform(); for( PrototypeAsteroid asteroid : asteroids ) { asteroid.draw( (Graphics2D)g, view ); }}RandomAsteroidExample代码如下所示：
package javagames.prototype;import java.awt.*;import java.awt.event.KeyEvent;import java.util.*;import javagames.prototype.PrototypeAsteroid.Size;import javagames.util.*;
public class RandomAsteroidExample extends SimpleFramework { private PrototypeAsteroidFactory factory; private ArrayList asteroids; private Random rand; public RandomAsteroidExample() { appBorderScale = 0.9f; appWidth = 640; appHeight = 640; appMaintainRatio = true; appSleep = 1L; appTitle = "Random Asteroids"; appBackground = Color.WHITE; appFPSColor = Color.BLACK; } @Override protected void initialize() { super.initialize(); rand = new Random(); asteroids = new ArrayList(); PolygonWrapper wrapper = new PolygonWrapper( appWorldWidth, appWorldHeight ); factory = new PrototypeAsteroidFactory( wrapper ); createAsteroids(); } private void createAsteroids() { asteroids.clear(); for( int i = 0; i < 42; ++i ) { asteroids.add( getRandomAsteroid() ); } } private PrototypeAsteroid getRandomAsteroid() { float x = rand.nextFloat() * 2.0f - 1.0f; float y = rand.nextFloat() * 2.0f - 1.0f; Vector2f position = new Vector2f( x, y ); Size[] sizes = Size.values(); Size randomSize = sizes[ rand.nextInt( sizes.length ) ]; switch( randomSize ) { case Small: return factory.createSmallAsteroid( position ); case Medium: return factory.createMediumAsteroid( position ); case Large: default: return factory.createLargeAsteroid( position ); } } @Override protected void processInput( float delta ) { super.processInput( delta ); if( keyboard.keyDownOnce( KeyEvent.VK_ESCAPE ) ) { createAsteroids(); } } @Override protected void updateObjects( float delta ) { super.updateObjects( delta ); for( PrototypeAsteroid asteroid : asteroids ) { asteroid.update( delta ); } } @Override protected void render( Graphics g ) { super.render( g ); g.drawString( "Press ESC to respawn", 20, 35 ); Matrix3x3f view = getViewportTransform(); for( PrototypeAsteroid asteroid : asteroids ) { asteroid.draw( (Graphics2D)g, view ); } } public static void main( String[] args ) { launchApp( new RandomAsteroidExample() ); }}`
